package com.yu.config.uuid;

import cn.hutool.core.date.SystemClock;

import java.util.concurrent.atomic.AtomicLong;

public class Snowflake {

    private final long twepoch = 1288834974657L;
    private final long workerIdBits = 1L;
    private final long datacenterIdBits = 1L;
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private final long sequenceBits = 8L;
    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    private long workerId;
    private long datacenterId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    private final AtomicLong seq = new AtomicLong();

    /**
     * 构造
     * @param workerId 终端ID
     * @param datacenterId 数据中心ID
     */
    public Snowflake(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    /**
     * 下一个ID
     * @return ID
     */
    public synchronized long nextId() {
        long timestamp = SystemClock.now();
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        Long id = ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;

        return id + seq.getAndIncrement();
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = SystemClock.now();
        while (timestamp <= lastTimestamp) {
            timestamp = SystemClock.now();
        }
        return timestamp;
    }
}
